1. Field of the Invention:
The present invention relates to a printer and more particularly to a mechanism for adjusting a gap (hereafter referred to as a platen gap) between a platen and a printing head.
2. Description of the Prior Art:
A printer is known wherein a carriage having a printing head mounted thereon is movably mounted on a guide shaft, and with the printing head moved parallel to a platen, characters are printed on a printing paper held on the platen.
A printer of this type must ensure that the platen gap is of proper size to assure high quality printing and thus includes a platen gap adjusting mechanism.
Such a platen gap adjusting mechanism is described for example in Japanese Laid-Open Patent Publication No. 58-90975. According to this platen gap adjusting mechanism, an eccentric bushing is rotatably fitted in a carriage, a guide shaft penetrates the bushing, and the printing head is moved integrally with the bushing and carriage to adjust the platen gap.
Another example of a platen gap adjusting mechanism is described in Japanese Laid-Open Utility Model Publication No. 58-175951. With this platen gap adjusting mechanism, the thrust bearing member one of two guide shafts is made eccentric and is rotatably engaged with the carriage, and the eccentric bearing is arbitrarily rotated to adjust the plate gap.
However, such a platen gap adjusting mechanism suffers from the disadvantages that: (1) adjustment with the eccentric bush is difficult, and (2) the mechanism is complicated and thus expensive.
Furthermore, a serial printer is known and described in Japanese Laid-Open Utility Model Publication No. 58-28851.
The serial printer includes a guide rail having rack teeth formed over the surface of a rack and disposed parallel to a platen for supporting a printing paper. A printing head has a motor, a pinion is fixedly mounted on a rotary shaft of the motor, and a guide piece is formed on the bottom surface of the printing head. The pinion of the motor and the rack of the guide rail are intermeshed to hold the guide rail between the pinion and the guide piece. Upon rotation of the motor, the motor and the printing head are integrally moved on the guide rail due to thrust force caused by engagement between the pinion and the rack, and thereby printing is effected.
However, such a printer suffers from the disadvantage that the guide rail is held between the pinion fixedly mounted on the rotary shaft of the motor and the guide piece formed on the bottom surface of the printing head. As a result, the printing head cannot be moved perpendicularly to the axial direction of the platen. Therefore, adjustment of the platen gap is very difficult.